1. Field of the Invention
The invention relates to novel 2,5-di- and 2,3,5-trisubstituted pyridines and to processes for their preparation from nicotine.
2. Background Art
2,5-disubstituted (or, in the case of alternative numbering, 3,6-disubstituted) pyridines such as, 6-hydroxynicotinic or 6-chloronicotinic acid, are valuable chemical intermediates, for example, for the preparation of retinoid analogues (U.S. Pat. No. 5,089,509) or renin inhibitors (U.S. Pat. No. 5,098,924).
The 2,5-disubstituted pyridines which could be obtained to date on an industrial scale are compounds which, like 6-hydroxynicotinic acid, as a rule have attached one C.sub.1 radical only in the 5- (or 3-) position.
To prepare compounds having longer carbon chains, this C.sub.1 radical must be extended by means of conventional synthetic methods with C-C coupling (U.S. Pat. No. 5,089,509, column 13). Since this method is complicated and expensive, it was desirable to obtain compounds having longer side chains and functional groups which can be used for further synthetic steps in a simpler fashion. It was, furthermore, desirable to make accessible compounds of this class which have attached to them a chlorine atom as an additional substituent in the 3-position of the pyridine ring (if numbered as 2-pyridone).